Natural gas liquid fractionation plant waste heat conversion to power using dual turbines organic rankine cycle

ABSTRACT

Certain aspects of a natural gas liquid fractionation plant waste heat conversion to power using dual turbines Organic Rankine Cycle can be implemented as a first heating fluid circuit thermally coupled to first multiple heat sources of a natural gas liquid (NGL) fractionation plant, a second heating fluid circuit thermally coupled to second multiple heat sources of the NGL fractionation plant, and two power generation systems, each including an organic Rankine cycle (ORC). A control system actuates a first set of control valves to selectively thermally couple the first heating fluid circuit to at least a portion of the first multiple heat sources of the NGL fractionation plant, and to actuate a second set of control valves to selectively thermally couple the second heating fluid circuit to at least a portion of the second multiple heat sources of the NGL fractionation plant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims priority under 35 U.S.C. § 120 to, U.S. patent application Ser. No. 15/842,382 entitled “Natural Gas Liquid Fractionation Plant Waste Heat Conversion to Power Using Dual Turbines Organic Rankine Cycle,” which was filed on Dec. 14, 2017, which in turn claims the benefit of priority to U.S. Provisional Application Ser. No. 62/542,687 entitled “Utilizing Waste Heat Recovered From Natural Gas Liquid Fractionation Plants,” which was filed on Aug. 8, 2017. The entire contents of both previous applications are incorporated herein by reference.

TECHNICAL FIELD

This disclosure relates to operating industrial facilities, for example, a natural gas liquid fractionation plant or other industrial facilities that include operating plants that generate heat, for example, a natural gas liquid fractionation plant.

BACKGROUND

Natural gas liquid (NGL) processes are chemical engineering processes and other facilities used in petroleum refineries to transform natural gas into products, for example, liquefied petroleum gas (LPG), gasoline, kerosene, jet fuel, diesel oils, fuel oils, and such products. NGL facilities are large industrial complexes that involve many different processing units and auxiliary facilities, for example, utility units, storage tanks, and such auxiliary facilities. Each refinery can have its own unique arrangement and combination of refining processes determined, for example, by the refinery location, desired products, economic considerations, or such factors. The NGL processes that are implemented to transform the natural gas into the products such as those listed earlier can generate heat, which may not be reused, and byproducts, for example, greenhouse gases (GHG), which may pollute the atmosphere. It is believed that the world's environment has been negatively affected by global warming caused, in part, due to the release of GHG into the atmosphere.

SUMMARY

This specification describes technologies relating to cooling capacity generation, power generation or potable water production from waste heat in a natural gas liquid (NGL) fractionation plant.

The present disclosure includes one or more of the following units of measure with their corresponding abbreviations, as shown in Table 1:

TABLE 1 Unit of Measure Abbreviation Degrees Celsius ° C. Megawatts MW One million MM British thermal unit Btu Hour hr. or H Pounds per square inch (pressure) psi Kilogram (mass) Kg Second S Cubic meters per day m³/day Fahrenheit F.

In a general implementation, a system includes a first heating fluid circuit thermally coupled to first multiple heat sources of a natural gas liquid (NGL) fractionation plant; a second heating fluid circuit thermally coupled to second multiple heat sources of the NGL fractionation plant; a first power generation system that includes a first organic Rankine cycle (ORC), which includes (i) a first portion of a working fluid that is thermally coupled to the first heating fluid circuit to heat the first portion of the working fluid, and (ii) a first expander configured to generate electrical power from the heated first portion of the working fluid; a second power generation system that includes a second organic Rankine cycle (ORC), which includes (i) a second portion of the working fluid that is thermally coupled to the first and second heating fluid circuits to heat the second portion of the working fluid, and (ii) a second expander configured to generate electrical power from the heated second portion of the working fluid; and a control system configured to actuate a first set of control valves to selectively thermally couple the first heating fluid circuit to at least a portion of the first multiple heat sources of the NGL fractionation plant, and to actuate a second set of control valves to selectively thermally couple the second heating fluid circuit to at least a portion of the second multiple heat sources of the NGL fractionation plant.

In an aspect combinable with the general implementation, the first portion of the working fluid is thermally coupled to the first heating fluid circuit in an evaporator of the first ORC.

In another aspect combinable with any of the previous aspects, the second portion of the working fluid is thermally coupled to the first and second heating fluid circuits in an evaporator of the second ORC.

In another aspect combinable with any of the previous aspects, The system includes a heating fluid tank that is fluidly coupled to the evaporators of the first and second ORCs.

In another aspect combinable with any of the previous aspects, the working fluid includes isobutene.

In another aspect combinable with any of the previous aspects, the first and second heating fluid circuits include water or oil.

In another aspect combinable with any of the previous aspects, the system includes a condenser fluidly coupled to the first and second expanders and to a condenser fluid source to cool the working fluid, a first pump to circulate the first portion of the working fluid through the first ORC, a second pump to circulate the second portion of the working fluid through the second ORC.

In another aspect combinable with any of the previous aspects, the first multiple heat sources include a first portion of sub-units of the NGL fractionation plant that includes an ethane system, a second multiple sub-units of the NGL fractionation plant that includes a propane system, a third portion of sub-units of the NGL fractionation plant that includes a butane system, a fourth portion of sub-units of the NGL fractionation plant that includes a natural gasoline system, and a fifth portion of sub-units of the NGL fractionation plant that includes a solvent regeneration system.

In another aspect combinable with any of the previous aspects, the first portion of sub-units of the NGL fractionation plant includes at least one ethane system heat source including a first ethane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of an ethane dryer.

In another aspect combinable with any of the previous aspects, the second portion of sub-units of the NGL fractionation plant includes at least three propane system heat sources including a first propane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a propane dehydrator, a second propane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a propane vapor recovery compressor stream, a third propane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a propane main compressor stream.

In another aspect combinable with any of the previous aspects, the third portion of sub-units of the NGL fractionation plant includes at least two butane system heat sources including a first butane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a butane dehydrator, and a second butane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a debutanizer bottoms.

In another aspect combinable with any of the previous aspects, the fourth portion of sub-units of the NGL fractionation plant includes at least two natural gasoline system heat sources including a first natural gasoline system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a natural gasoline decolorizer overhead stream, and a second natural gasoline system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a Reid vapor pressure control column overhead stream.

In another aspect combinable with any of the previous aspects, the fifth portion of sub-units of the NGL fractionation plant includes at least two solvent regeneration system heat sources including a first solvent regeneration system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of an ADIP regeneration section overhead stream, and a second solvent regeneration system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of an ADIP regeneration section bottoms.

In another aspect combinable with any of the previous aspects, the second multiple heat sources include a first portion of sub-units of the NGL fractionation plant that includes an ethane system, a second multiple sub-units of the NGL fractionation plant that includes a propane system, a third portion of sub-units of the NGL fractionation plant that includes a butane system, a fourth portion of sub-units of the NGL fractionation plant that includes a pentane system, and a fifth portion of sub-units of the NGL fractionation plant that includes a natural gasoline system.

In another aspect combinable with any of the previous aspects, the first portion of sub-units of the NGL fractionation plant includes at least one ethane system heat source including a first ethane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a deethanizer refrigeration compressor.

In another aspect combinable with any of the previous aspects, the second portion of sub-units of the NGL fractionation plant includes at least two propane system heat sources including a first propane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a depropanizer overhead stream, and a second propane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a propane refrigeration compressor stream.

In another aspect combinable with any of the previous aspects, the third portion of sub-units of the NGL fractionation plant includes at least two butane system heat sources that includes a first butane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a debutanizer overhead stream, and a second butane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a butane refrigeration compressor stream.

In another aspect combinable with any of the previous aspects, the fourth portion of sub-units of the NGL fractionation plant includes at least one pentane system heat source including a first pentane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a depentanizer overhead stream.

In another aspect combinable with any of the previous aspects, the fifth portion of sub-units of the NGL fractionation plant includes at least one natural gasoline system heat source including a first natural gasoline system heat source that comprises a heat exchanger that is thermally coupled to an outlet stream of a natural gasoline decolorizing section pre-flash drum overhead stream.

In another general implementation, a method of recovering heat energy generated by a NGL fractionation plant includes circulating a first heating fluid through a first heating fluid circuit thermally coupled to first multiple heat sources of a natural gas liquid (NGL) fractionation plant; circulating a second heating fluid is circulated through a second heating fluid circuit thermally coupled to a second plurality of heat sources of the NGL fractionation plant; generating electrical power through a first power generation system that includes a first organic Rankine cycle (ORC), which includes (i) a first portion of a working fluid that is thermally coupled to the first heating fluid circuit to heat the first portion of the working fluid, and (ii) a first expander configured to generate electrical power from the heated first portion of the working fluid; generating electrical power is generated through a second power generation system that includes a second organic Rankine cycle (ORC), which includes (i) a second portion of the working fluid that is thermally coupled to the first and second heating fluid circuits to heat the second portion of the working fluid, and (ii) a second expander configured to generate electrical power from the heated second portion of the working fluid; actuating, with a control system, a first set of control valves to selectively thermally couple the first heating fluid circuit to at least a portion of the first multiple heat sources of the NGL fractionation plant; and actuating, with the control system, a second set of control valves to selectively thermally couple the second heating fluid circuit to at least a portion of the second multiple heat sources of the NGL fractionation plant.

In an aspect combinable with the general implementation, the first portion of the working fluid is thermally coupled to the first heating fluid circuit in an evaporator of the first ORC.

In another aspect combinable with any of the previous aspects, The second portion of the working fluid is thermally coupled to the first and second heating fluid circuits in an evaporator of the second ORC.

In another aspect combinable with any of the previous aspects, the system includes a heating fluid tank that is fluidly coupled to the evaporators of the first and second ORCs.

In another aspect combinable with any of the previous aspects, the working fluid includes isobutene.

In another aspect combinable with any of the previous aspects, the first and second heating fluid circuits include water or oil.

In another aspect combinable with any of the previous aspects, the system includes a condenser fluidly coupled to the first and second expanders and to a condenser fluid source to cool the working fluid, a first pump to circulate the first portion of the working fluid through the first ORC, a second pump to circulate the second portion of the working fluid through the second ORC.

In another aspect combinable with any of the previous aspects, the first multiple heat sources include a first portion of sub-units of the NGL fractionation plant that includes an ethane system, a second multiple sub-units of the NGL fractionation plant that includes a propane system, a third portion of sub-units of the NGL fractionation plant that includes a butane system, a fourth portion of sub-units of the NGL fractionation plant that includes a natural gasoline system, and a fifth portion of sub-units of the NGL fractionation plant that includes a solvent regeneration system.

In another aspect combinable with any of the previous aspects, the first portion of sub-units of the NGL fractionation plant includes at least one ethane system heat source including a first ethane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of an ethane dryer.

In another aspect combinable with any of the previous aspects, the second portion of sub-units of the NGL fractionation plant includes at least three propane system heat sources including a first propane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a propane dehydrator, a second propane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a propane vapor recovery compressor stream, a third propane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a propane main compressor stream.

In another aspect combinable with any of the previous aspects, the third portion of sub-units of the NGL fractionation plant includes at least two butane system heat sources including a first butane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a butane dehydrator, and a second butane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a debutanizer bottoms.

In another aspect combinable with any of the previous aspects, the fourth portion of sub-units of the NGL fractionation plant includes at least two natural gasoline system heat sources including a first natural gasoline system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a natural gasoline decolorizer overhead stream, and a second natural gasoline system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a Reid vapor pressure control column overhead stream.

In another aspect combinable with any of the previous aspects, the fifth portion of sub-units of the NGL fractionation plant includes at least two solvent regeneration system heat sources including a first solvent regeneration system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of an ADIP regeneration section overhead stream, and a second solvent regeneration system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of an ADIP regeneration section bottoms.

In another aspect combinable with any of the previous aspects, the second multiple heat sources include a first portion of sub-units of the NGL fractionation plant that includes an ethane system, a second multiple sub-units of the NGL fractionation plant that includes a propane system, a third portion of sub-units of the NGL fractionation plant that includes a butane system, a fourth portion of sub-units of the NGL fractionation plant that includes a pentane system, and a fifth portion of sub-units of the NGL fractionation plant that includes a natural gasoline system.

In another aspect combinable with any of the previous aspects, the first portion of sub-units of the NGL fractionation plant includes at least one ethane system heat source including a first ethane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a deethanizer refrigeration compressor.

In another aspect combinable with any of the previous aspects, the second portion of sub-units of the NGL fractionation plant includes at least two propane system heat sources including a first propane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a depropanizer overhead stream, and a second propane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a propane refrigeration compressor stream.

In another aspect combinable with any of the previous aspects, the third portion of sub-units of the NGL fractionation plant includes at least two butane system heat sources that includes a first butane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a debutanizer overhead stream, and a second butane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a butane refrigeration compressor stream.

In another aspect combinable with any of the previous aspects, the fourth portion of sub-units of the NGL fractionation plant includes at least one pentane system heat source including a first pentane system heat source that includes a heat exchanger that is thermally coupled to an outlet stream of a depentanizer overhead stream.

In another aspect combinable with any of the previous aspects, the fifth portion of sub-units of the NGL fractionation plant includes at least one natural gasoline system heat source including a first natural gasoline system heat source that comprises a heat exchanger that is thermally coupled to an outlet stream of a natural gasoline decolorizing section pre-flash drum overhead stream.

The details of one or more implementations of the subject matter described in this specification are set forth in the accompanying drawings and the detailed description. Other features, aspects, and advantages of the subject matter will become apparent from the description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram of a dual organic Rankine cycle (ORC) based waste heat to power conversion plant that uses waste heat from one or more heat sources in a NGL fractionation plant.

FIG. 1B is a diagram of deethanizer section waste heat recovery system in a NGL plant.

FIG. 1C is a diagram of a propane dehydrator section waste heat recovery system in a NGL plant.

FIG. 1D is a diagram of a depropanizer section waste heat recovery system in a NGL plant.

FIG. 1E is a diagram of a butane dehydrator section waste heat recovery system in a NGL plant.

FIG. 1F is a diagram of a debutanizer section waste heat recovery system in a NGL plant.

FIG. 1G is a diagram of a depentanizer section waste heat recovery system in a NGL plant.

FIG. 1H is a diagram of a solvent regeneration section waste heat recovery system in a NGL plant.

FIG. 1I is a diagram of a natural gasoline decolorizing section waste heat recovery system in a NGL plant.

FIG. 1J is a diagram of a propane tank recovery section waste heat recovery system in a NGL plant.

FIG. 1K is a diagram of propane product refrigeration section waste heat recovery system in a NGL plant.

FIG. 1L is a diagram of propane product sub-cooling section waste heat recovery system in a NGL plant.

FIG. 1M is a diagram of butane product refrigeration section waste heat recovery system in a NGL plant.

FIG. 1N is a diagram of ethane production section waste heat recovery system in a NGL plant.

FIG. 1O is a diagram of natural gasoline vapor section waste heat recovery system in a NGL plant.

DETAILED DESCRIPTION

NGL Plant

Gas processing plants can purify raw natural gas or crude oil production associated gases (or both) by removing common contaminants such as water, carbon dioxide and hydrogen sulfide. Some of the substances which contaminate natural gas have economic value and can be processed or sold or both. Upon the separation of methane gas, which is useful as sales gas for houses and power generation, the remaining hydrocarbon mixture in liquid phase is called natural gas liquids (NGL). The NGL is fractionated in a separate plant or sometimes in the same gas processing plant into ethane, propane and heavier hydrocarbons for several versatile uses in chemical and petrochemical as well as transportation industries. The NGL fractionation plant uses the following processes or sections: fractionation, product treating, and natural gasoline processing. The fractionation processes or sections can include heat sources (also commonly referred to as streams) including, but not limited to, a propane condenser, a propane refrigerant condenser, a naphtha cooler, a depentanizer condenser, an amine-di-iso-propanol (ADIP) cooler, a regenerator overhead (OVHD) condenser, a Reid vapor pressure (RVP) column condenser, a depropanizer condenser, a debutanizer condenser, or combinations thereof. The product treating processes or sections can include the following non-limiting heat sources: a propane dehydrator condenser, a butane dehydrator condenser, a propane condenser, an air-cooled condenser, a regeneration gas cooler, and a butane condenser, or combinations thereof. The natural gasoline processing processes or sections can include, but are not limited to, a natural gasoline (NG) flash vapor condenser, a NG decolorizer condenser, or combinations thereof

Fractionation Section

Fractionation is the process of separating the different components of natural gas. Separation is possible because each component has a different boiling point. At temperatures less than the boiling point of a particular component, that component condenses to a liquid. It is also possible to increase the boiling point of a component by increasing the pressure. By using columns operating at different pressures and temperatures, the NGL fractionation plant is capable of separating ethane, propane, butane, pentane, or combinations thereof (with or without heavier associated hydrocarbons) from NGL fractionation feeds. Deethanizing separates ethane from C2+ NGL, where C2 refers to a molecule containing two carbon atoms (ethane), and where C2+ refers to a mixture containing molecules having two or more carbon atoms, for example, a NGL containing C2, C3, C4, C5 can be abbreviated as “C2+ NGL.” Depropanizing and debutanizing separate propane and butane, respectively, from C3+ NGL and C4+ NGL, respectively. Because the boiling points of heavier natural gases are closer to each other, such gases can be harder to separate compared to lighter natural gases. Also, a rate of separation of heavier components is less than that of comparatively lighter components. In some instances, the NGL fractionation plant can implement, for example, about 45 distillation trays in the deethanizer, about 50 trays in the depropanizer, and about 55 trays in the debutanizer.

The fractionation section can receive a feed gas containing C2+ NGL from gas plants, which are upstream plants that condition and sweeten the feed gas, and produce a sales gas, such as a C1/C2 mixture, where C1 is about 90%, as a final product. The C2+ NGL from gas plants can be further processed in the NGL fractionation plant for C2+ recovery. From feed metering or surge unit metering (or both), feed flows to the three fractionation modules, namely, the deethanizing module, the depropanizing module and the debutanizing module, each of which is described later.

Deethanizer Module (or Deethanizer Column)

The C2+ NGL is pre-heated before entering the deethanizer column for fractionation. The separated ethane leaves the column as overhead gas. The ethane gas is condensed by a closed-loop propane refrigeration system. After being cooled and condensed, the ethane is a mixture of gas and liquid. The liquid ethane is separated and pumped back to the top of the column as reflux. The ethane gas is warmed in an economizer and then sent to users. The bottoms product from the deethanizer reboiler is C3+ NGL, which is sent to the depropanizer module.

Depropanizer Module (or Depropanizer Column)

From the deethanizer module, C3+ NGL enters the depropanizer module for fractionation. The separated propane leaves the column as overhead gas. The gas is condensed using coolers. The propane condensate is collected in a reflux drum. Some of the liquid propane is pumped back to the column as reflux. The rest of the propane is either treated or sent to users as untreated product. The bottoms product from the depropanizer reboiler, C4+ is then sent to the debutanizer module

Debutanizer Module (or Debutanizer Column)

C4+ enters the debutanizer module for fractionation. The separated butane leaves the column as overhead gas. The gas is condensed using coolers. The butane condensate is collected in a reflux drum. Some of the liquid butane is pumped back to the column as reflux. The rest of the butane is either treated or sent to users as untreated product. The bottoms product from the debutanizer reboiler, C5+ natural gas (NG) goes on to a RVP control section (which may also be referred to as a rerun unit), which will be discussed in greater detail in a later section.

Product Treating Section

While ethane requires no further treatment, propane and butane products are normally treated to remove hydrogen sulfide (H₂S), carbonyl sulfide (COS), and mercaptan sulfur (RSH). Then, the products are dried to remove any water. All exported product is treated, while untreated products can go to other industries. As described later, propane receives ADIP treating, MEROX™ (Honeywell UOP; Des Plaines, Ill.) treating, and dehydration. Butane receives MEROX treating, and dehydration.

ADIP Treating Section

ADIP is a solution of di-isopropanol amine and water. ADIP treating extracts H₂S and COS from propane. The ADIP solution, through contact with the sour propane, absorbs the H₂S and COS. The ADIP solution first contacts the sour propane in an extractor. In the extractor, the ADIP absorbs most of the H₂S and some of the COS. The propane then passes through a mixer/settler train where the propane contacts with ADIP solution to extract more H₂S and COS. This partially sweetened propane is cooled and then washed with water to recover the ADIP entrained with the propane. The propane is then sent to MEROX treating, which is described later. The rich ADIP that has absorbed the H₂S and COS leaves the bottom of the extractor and is regenerated into lean ADIP for reuse. The regenerator column has a temperature and pressure that are suitable for acid gas removal. When the rich ADIP enters the regenerator, the entrained acid gases are stripped. As the acid gases leaves the regenerator as overhead, any free water is removed to prevent acid formation. The acid gases are then sent to flare. The lean ADIP leaves the extractor bottom and is cooled and filtered. Lean ADIP returns to the last mixer/settler and flows back through the system in the counter-current direction of the propane to improve contact between the propane and ADIP, which improves H₂S and COS extraction.

C3/C4 MEROX Treating Section

MEROX treating removes mercaptan sulfur from C3/C4 product. Mercaptans are removed using a solution of sodium hydroxide (NaOH), also known by the commercial name caustic soda (hereinafter referred to as “caustic”) and MEROX. The MEROX catalyst facilitates the oxidation of mercaptans to disulfides. The oxidation takes place in an alkaline environment, which is provided by using the caustic solution. MEROX treating for C3 and C4 is similar. Both products are prewashed with caustic to remove any remaining traces of H₂S, COS, and CO₂. This prevents damage to the caustic that is used in MEROX treating. After prewashing, product flows to an extractor, where a caustic solution with MEROX catalyst contacts with the product. The caustic/catalyst solution converts the mercaptans into mercaptides. The sweetened product, which is lean on acid gases, leaves the extractor as overhead and any remaining caustic is separated. Caustic leaves the bottom of both product extractors rich with mercaptides. The rich caustic is regenerated into lean caustic for reuse. The C3/C4 extraction sections share a common caustic regeneration section, namely, an oxidizer. Before entering the bottom of the oxidizer, the rich caustic is injected with MEROX catalyst to maintain proper catalyst concentration, heated, and mixed with process air. In the oxidizer, the mercaptides are oxidized into disulfides. The mixture of disulfides, caustic, and air leave the oxidizer as overhead. The air, disulfide gases, and disulfide oil are separated from the regenerated caustic. The regenerated caustic is pumped to the C3/C4 extractor. Regenerated caustic with any residual disulfides is washed with NG in the NG wash settler.

C3/C4 Dehydration Section

Propane or butane products (or both) contain water when they leave MEROX treating. Dehydration removes moisture in such products through adsorption before the products flow to refrigeration and storage. The dehydration processes for C3 and C4 are similar. Both C3/C4 dehydration sections have two dehydrators containing molecular sieve desiccant beds. One dehydrator is in service while the other undergoes regeneration. Regeneration consists of heating the sieve beds to remove moisture, then cooling the beds before reuse. During drying, product flows up and through the molecular sieve bed, which adsorbs (that is, binds to its surface) moisture. From the top of the dehydrator, dry C3/C4 products flow to refrigeration.

Natural Gasoline (NG) Processing Section

NG processing includes RVP control, decolorizing and depentanizing sections.

RVP Control Section

A Reid vapor pressure (RVP) control section (or rerun unit) is a fractionator column that receives the C5+ NG from the debutanizer bottom. The RVP control section collects a pentane product. The RVP control section can be used to adjust the RVP of the pentane product at a rerun fractionator overhead before the pentane product is sent to a pentane storage tank. RVP is a measure of the ability of a hydrocarbon to vaporize. RVP (sometimes called volatility) is an important specification in gasoline blending. The RVP control section stabilizes the RVP of NG by removing small amounts of pentane. Depending on operational requirements, the RVP control section can be totally or partially bypassed. NG from the debutanizer bottoms goes to the RVP column where a controlled amount of pentane is stripped and leaves the column as overhead gas. As in NGL fractionation, the overhead gas is condensed with coolers, and some of the condensate is pumped back to the column as reflux. The remaining pentane is cooled and sent to storage. If the RVP column bottoms product (NG) meets color specifications, it is sent to storage. If not, it is sent to decolorizing.

Decolorizing Section

The decolorizing section removes color bodies from NG. Color bodies are traces of heavy ends found in the debutanizer bottoms product. Other impurities such as corrosion products from the pipeline may also be present. These must be removed for NG to meet the color specification. Decolorizer feed can be RVP column bottoms product or debutanizer bottoms product, or a combination of both. Additional natural gasoline can also be supplied from other facilities to maintain a hexane plus (C6+) product supply. If decolorizing is needed, NG first passes through a pre-flash-drum. A large portion of the lighter NG components vaporizes and leaves the drum as overhead. The heavier NG components remain along with the color bodies and are fed to the decolorizer column, where the remaining color bodies are separated. The NG leaves the decolorizer as overhead gas and is condensed and collected in the NG product drum, with some pumped back to the column as reflux. Overhead from the column and flash drum are joined and pumped to either the depentanizer (described later) or cooled and sent to storage in the feed product surge unit. The color bodies leave the decolorizer as bottoms product and are pumped to the feed and surge unit to be injected into a crude line.

Depentanizing Section

Depentanizing uses a fractionation column to produce a pentane overhead product and a C6+ bottoms product. Both the pentane product and the C6+ bottoms product are separately fed to storage or downstream the petrochemical plants. The feed to the depentanizer is the NG product stream from the decolorizing section. Feed can be increased or decreased based on the demand for C6+ bottoms product. If the NGL fractionation plant NG production cannot meet demand, NG can be imported from oil refineries. The decolorized NG is preheated before entering the depentanizer. The separated pentane leaves the column as overhead gas. The overhead condensers cool the overhead stream, and some is pumped back to the column as reflux. The remaining pentane is cooled and sent to storage. Light NG in the bottoms is vaporized and returned to heat the depentanizer. The remaining bottoms product is cooled and sent to storage as C6+.

Table 2 lists duty per train of major waste heat streams in an example of an NGL fractionation plant.

TABLE 2 Duty/train Stream Name (MMBtu/h) Propane refrigerant condenser 94 Propane dehydration condenser 22 Butane dehydrator condenser 9 Naphtha cooler 11 Depentanizer condenser 100 ADIP cooler 73 Regenerator OVHD condenser 18 NG flash vapor condenser 107 NG decolorizer condenser 53 Natural gasoline (cooling) process propane 29 condenser Fractionation propane condenser 81 Air cooled condenser 16 Regeneration gas cooler 22 RVP column condenser 36 Butane condenser 49 Depropanizer condenser 194 Debutanizer condenser 115

In Table 2, “Duty/train” represents each stream's thermal duty in millions Btu per hour (MMBtu/h) per processing train. A typical NGL fractionation plant includes three to four processing trains.

The systems described in this disclosure can be integrated with a NGL fractionation plant to make the fractionation plant more energy efficient or less polluting or both. In particular, the energy conversion system can be implemented to recover low grade waste heat from the NGL fractionation plant. Low grade waste heat is characterized by a temperature difference between a source and sink of the low grade heat steam being between 65° C. and 232° C. (150° F. and 450° F.). The NGL fractionation plant is an attractive option for integration with energy conversion systems due to a large amount of low grade waste heat generated by the plant and an absence of a need for deep cooling. Deep cooling refers to a temperature that is less than ambient that uses a refrigeration cycle to maintain.

The low grade waste heat from an NGL fractionation plant can be used for commodities such as carbon-free power generation, cooling capacity generation, potable water production from sea water, or combinations thereof. Low grade waste heat is characterized by a temperature ranging between 65° C. and 232° C. (150° F. to 450° F.). The waste heat can be used for the mono-generation, co-generation, or tri-generation of one or more or all of the commodities mentioned earlier. Low grade waste heat from the NGL fractionation plant can be used to provide in-plant sub-ambient cooling, thus reducing the consumption of power or fuel (or both) of the plant. Low grade waste heat from the NGL fractionation plant can be used to provide ambient air conditioning or cooling in the industrial community or in a nearby non-industrial community, thus helping the community to consume energy from alternative sources. In addition, the low grade waste heat can be used to desalinate water and produce potable water to the plant and adjacent community. An NGL fractionation plant is selected for low grade waste heat recovery because of a quantity of low grade waste heat available from the NGL fractionation plant as well as a cooling requirement of the plant to ambient temperature cooling (instead of deep cooling).

The energy conversion systems described in this disclosure can be integrated into an existing NGL fractionation plant as a retrofit or can be part of a newly constructed NGL fractionation plant. A retrofit to an existing NGL fractionation plant allows the carbon-free power generation, and fuel savings advantages offered by the energy conversion systems described here to be accessible with a reduced capital investment. For example, the energy conversion systems described here can produce one or more or all of substantially between 35 MW and 40 MW (for example, 37 MW) of carbon-free power, substantially between 100,000 and 150,000 m³/day (for example, 120,000 m³/day) of desalinated water, and substantially between 350 MM BTU/h and 400 MM BTU/h (for example, 388 MM BTU/h) of cooling capacity for in-plant or community utilization or both.

As described later, the systems for waste heat recovery and re-use from the NGL fractionation plant can include modified multi-effect distillation (MED) systems, customized Organic Rankine Cycle (ORC) systems, unique ammonia-water mixture Kalina cycle systems, customized modified Goswami cycle systems, mono-refrigerant specific vapor compression-ejector-expander triple cycle systems, or combinations of one or more of them. Details of each disclosure are described in the following paragraphs.

Heat Exchangers

In the configurations described in this disclosure, heat exchangers are used to transfer heat from one medium (for example, a stream flowing through a plant in a NGL fractionation plant, a buffer fluid or other medium) to another medium (for example, a buffer fluid or different stream flowing through a plant in the NGL fractionation plant). Heat exchangers are devices which transfer (exchange) heat typically from a hotter fluid stream to a relatively less hotter fluid stream. Heat exchangers can be used in heating and cooling applications, for example, in refrigerators, air conditions or such cooling applications. Heat exchangers can be distinguished from one another based on the direction in which fluids flow. For example, heat exchangers can be parallel-flow, cross-flow or counter-current. In parallel-flow heat exchangers, both fluid involved move in the same direction, entering and exiting the heat exchanger side-by-side. In cross-flow heat exchangers, the fluid path runs perpendicular to one another. In counter-current heat exchangers, the fluid paths flow in opposite directions, with one fluid exiting whether the other fluid enters. Counter-current heat exchangers are sometimes more effective than the other types of heat exchangers.

In addition to classifying heat exchangers based on fluid direction, heat exchangers can also be classified based on their construction. Some heat exchangers are constructed of multiple tubes. Some heat exchangers include plates with room for fluid to flow in between. Some heat exchangers enable heat exchange from liquid to liquid, while some heat exchangers enable heat exchange using other media.

Heat exchangers in a NGL fractionation plant are often shell and tube type heat exchangers which include multiple tubes through which fluid flows. The tubes are divided into two sets—the first set contains the fluid to be heated or cooled; the second set contains the fluid responsible for triggering the heat exchange, in other words, the fluid that either removes heat from the first set of tubes by absorbing and transmitting the heat away or warms the first set by transmitting its own heat to the fluid inside. When designing this type of exchanger, care must be taken in determining the correct tube wall thickness as well as tube diameter, to allow optimum heat exchange. In terms of flow, shell and tube heat exchangers can assume any of three flow path patterns.

Heat exchangers in NGL facilities can also be plate and frame type heat exchangers. Plate heat exchangers include thin plates joined together with a small amount of space in between, often maintained by a rubber gasket. The surface area is large, and the corners of each rectangular plate feature an opening through which fluid can flow between plates, extracting heat from the plates as it flows. The fluid channels themselves alternate hot and cold liquids, meaning that the heat exchangers can effectively cool as well as heat fluid. Because plate heat exchangers have large surface area, they can sometimes be more effective than shell and tube heat exchangers.

Other types of heat exchangers can include regenerative heat exchangers and adiabatic wheel heat exchangers. In a regenerative heat exchanger, the same fluid is passed along both sides of the exchanger, which can be either a plate heat exchanger or a shell and tube heat exchanger. Because the fluid can get very hot, the exiting fluid is used to warm the incoming fluid, maintaining a near constant temperature. Energy is saved in a regenerative heat exchanger because the process is cyclical, with almost all relative heat being transferred from the exiting fluid to the incoming fluid. To maintain a constant temperature, a small quantity of extra energy is needed to raise and lower the overall fluid temperature. In the adiabatic wheel heat exchanger, an intermediate liquid is used to store heat, which is then transferred to the opposite side of the heat exchanger. An adiabatic wheel consists of a large wheel with threads that rotate through the liquids—both hot and cold—to extract or transfer heat. The heat exchangers described in this disclosure can include any one of the heat exchangers described earlier, other heat exchangers, or combinations of them.

Each heat exchanger in each configuration can be associated with a respective thermal duty (or heat duty). The thermal duty of a heat exchanger can be defined as an amount of heat that can be transferred by the heat exchanger from the hot stream to the cold stream. The amount of heat can be calculated from the conditions and thermal properties of both the hot and cold streams. From the hot stream point of view, the thermal duty of the heat exchanger is the product of the hot stream flow rate, the hot stream specific heat, and a difference in temperature between the hot stream inlet temperature to the heat exchanger and the hot stream outlet temperature from the heat exchanger. From the cold stream point of view, the thermal duty of the heat exchanger is the product of the cold stream flow rate, the cold stream specific heat and a difference in temperature between the cold stream outlet from the heat exchanger and the cold stream inlet temperature from the heat exchanger. In several applications, the two quantities can be considered equal assuming no heat loss to the environment for these units, particularly, where the units are well insulated. The thermal duty of a heat exchanger can be measured in watts (W), megawatts (MW), millions of British Thermal Units per hour (Btu/hr.), or millions of kilocalories per hour (Kcal/h). In the configurations described here, the thermal duties of the heat exchangers are provided as being “about X MW,” where “X” represents a numerical thermal duty value. The numerical thermal duty value is not absolute. That is, the actual thermal duty of a heat exchanger can be approximately equal to X, greater than X or less than X.

Flow Control System

In each of the configurations described later, process streams (also called “streams”) are flowed within each plant in a NGL fractionation plant and between plants in the NGL fractionation plant. The process streams can be flowed using one or more flow control systems implemented throughout the NGL fractionation plant. A flow control system can include one or more flow pumps to pump the process streams, one or more flow pipes through which the process streams are flowed and one or more valves to regulate the flow of streams through the pipes.

In some implementations, a flow control system can be operated manually. For example, an operator can set a flow rate for each pump and set valve open or close positions to regulate the flow of the process streams through the pipes in the flow control system. Once the operator has set the flow rates and the valve open or close positions for all flow control systems distributed across the NGL fractionation plant, the flow control system can flow the streams within a plant or between plants under constant flow conditions, for example, constant volumetric rate or such flow conditions. To change the flow conditions, the operator can manually operate the flow control system, for example, by changing the pump flow rate or the valve open or close position.

In some implementations, a flow control system can be operated automatically. For example, the flow control system can be connected to a computer system to operate the flow control system. The computer system can include a computer-readable medium storing instructions (such as flow control instructions and other instructions) executable by one or more processors to perform operations (such as flow control operations). An operator can set the flow rates and the valve open or close positions for all flow control systems distributed across the NGL fractionation plant using the computer system. In such implementations, the operator can manually change the flow conditions by providing inputs through the computer system. Also, in such implementations, the computer system can automatically (that is, without manual intervention) control one or more of the flow control systems, for example, using feedback systems implemented in one or more plants and connected to the computer system. For example, a sensor (such as a pressure sensor, temperature sensor or other sensor) can be connected to a pipe through which a process stream flows. The sensor can monitor and provide a flow condition (such as a pressure, temperature, or other flow condition) of the process stream to the computer system. In response to the flow condition exceeding a threshold (such as a threshold pressure value, a threshold temperature value, or other threshold value), the computer system can automatically perform operations. For example, if the pressure or temperature in the pipe exceeds the threshold pressure value or the threshold temperature value, respectively, the computer system can provide a signal to the pump to decrease a flow rate, a signal to open a valve to relieve the pressure, a signal to shut down process stream flow, or other signals.

FIGS. 1A-1O are schematic illustrations of a power generation system that utilizes waste heat from one or more heat sources in a natural gas liquid (NGL) fractionation plant.

FIG. 1A is a schematic diagram of an example system 300 to recover waste heat from heat sources in an NGL fractionation plant. FIGS. 1B-1O are schematic diagrams illustrating the location of the heat sources within the NGL fractionation plant, as well as the interaction (for example, fluid and thermal) with existing components of the NGL fractionation plant. In this example system 300, there are seventeen heat sources in the NGL fractionation plant. In this example system 300, the seventeen heat sources in the NGL fractionation plant are divided into two heating fluid circuits that, in some portions of the two circuits, are separated, and in other portions of the two circuits are combined. In this example system 300, one of the two heating fluid circuits serves only a first power generation system, while both heating fluid circuits serve a second power generation system.

Generally, the NGL fractionation plant contains a large amount of low grade waste heat. This waste heat can be used to produce water, cooling, power, or a combination of two or more. In some aspects, embodiments of the present disclosure include a system (such as system 300) that recovers the waste heat available in the NGL fractionation plant using a heat recovery network that includes multiple (for example, seventeen in some embodiments) heat exchangers distributed in particular areas of the NGL fractionation plant. In some embodiments, the system 300 can generate about 37 MW using dual organic Rankine cycle (ORC) systems. The low grade waste heat is recovered from processing units within the NGL fractionation using, for example, one or more buffer streams such as hot oil or pressurized water streams.

In example embodiments, the buffer streams flow from a storage tank at about 113° F. and are directed towards specific units in the NGL fractionation plant to recover particular amounts of thermal energy, as shown in FIGS. 1B-1O. The thermal energy absorbed from the NGL fractionation plant increases the buffer streams original temperature from about 113° F. to about 160° F. in a low temperature buffer stream and from about 113° F. to about 238° F. in a high temperature buffer stream. The buffer streams at 160° F. and 238° F. are then used as shown in FIG. 1A to produce about 37 MW using the dual ORC systems (described later). The buffer streams are reduced in temperature in the respective ORC systems to about 113° F. and flow back to the storage tank, where they are recombined.

FIG. 1A is a schematic diagram of the example system 300 to recover waste heat from the seventeen heat sources in the NGL fractionation plant. In some implementations, the system 300 can include a first heating fluid circuit 302 thermally coupled to a portion of the multiple heat sources. For example, the portion of multiple heat sources that are thermally coupled to the first heating fluid circuit 302 can include seven of the seventeen heat exchangers, including a first heat exchanger 302 a, a second heat exchanger 302 b, a third heat exchanger 302 c, a fourth heat exchanger 302 d, a fifth heat exchanger 302 e, a sixth heat exchanger 302 f, and a seventh heat exchanger 302 g. In some implementations, the seven heat sources can be connected in parallel (for example, relative to a flow of a buffer fluid). In some implementations, a single heat exchanger shown in a figure may illustrate one or more heat exchangers.

The system 300, as shown in FIG. 1A, can also include a second heating fluid circuit 304 thermally coupled to another portion of the multiple heat sources. For example, the portion of multiple heat sources that are thermally coupled to the second heating fluid circuit 304 can include ten of the seventeen heat exchangers, including a first heat exchanger 304 a, a second heat exchanger 304 b, a third heat exchanger 304 c, a fourth heat exchanger 304 d, a fifth heat exchanger 304 e, a sixth heat exchanger 304 f, a seventh heat exchanger 304 g, an eighth heat exchanger 304 h, a ninth heat exchanger 304 i, and a tenth heat exchanger 304 j. In some implementations, the ten heat sources can be connected in parallel (for example, relative to a flow of a buffer fluid). In some implementations, a single heat exchanger shown in a figure may illustrate one or more heat exchangers.

The example system 300 can include a first power generation system 314 that includes a first organic Rankine cycle (ORC). The first ORC can include a working fluid 316 that is thermally coupled to the second heating fluid circuit 304 to heat the working fluid 316. In some implementations, the working fluid 316 can be isobutane. The first ORC can also include a gas expander 320 configured to generate electrical power from the heated working fluid 316. As shown in FIG. 1A, the first ORC can additionally include an evaporator 318, a pump 324 and a condenser 322. In some implementations, the working fluid 316 can be thermally coupled to the second heating fluid circuit 304 in the evaporator 316.

The example system 300 also includes a second power generation system 326 that includes a second organic Rankine cycle (ORC). The second ORC can include a working fluid 328 that is thermally coupled to the first heating fluid circuit 302 and the second heating fluid circuit 304 to heat the working fluid 328. In some implementations, the working fluid 328 can be isobutane. The second ORC can also include a gas expander 332 configured to generate electrical power from the heated working fluid 328. As shown in FIG. 1A, the second ORC can additionally include an evaporator 330, a pump 334 and the condenser 322. In some implementations, the working fluid 328 can be thermally coupled to the first heating fluid circuit 302 and the second heating fluid circuit 304 in the evaporator 330.

In operation, a first heating fluid 306 (for example, water, oil, or such fluid) is circulated through the seven heat exchangers of the first heating fluid circuit 302. An inlet temperature of the first heating fluid 306 that is circulated into the inlets of each of the seven heat sources is the same or substantially the same subject to any temperature variations that may result as the heating fluid 306 flows through respective inlets. Each heat exchanger heats the heating fluid 306 to a respective temperature that is greater than the inlet temperature. The heated first heating fluid 306 from the seven heat exchangers are combined and then combined with a second heating fluid 308 at an outlet of the evaporator 318. The combined flows of the first and second heating fluids 306 and 308 are flowed through the evaporator 330 of the second ORC. Heat from the heated heating fluids 306 and 308 heats the working fluid 328 of the second ORC thereby increasing the working fluid temperature and evaporating the working fluid 328. The heat exchange with the working fluid 328 results in a decrease in the temperature of the combined flow of the first and second heating fluids 306 and 308. The combined flow of the first and second heating fluids 306 and 308 is then collected in a heating fluid tank 310 and can be pumped, by a pump 312, back through the seventeen heat exchangers of the first and second heating fluid circuits 302 and 304 to restart the waste heat recovery cycle.

In further operations, the second heating fluid 308 (for example, a fluid similar to or identical to the first heating fluid 306) is circulated through the ten heat exchangers of the second heating fluid circuit 304. An inlet temperature of the second heating fluid 308 that is circulated into the inlets of each of the ten heat sources is the same or substantially the same subject to any temperature variations that may result as the heating fluid 308 flows through respective inlets. Each heat exchanger heats the second heating fluid 308 to a respective temperature that is greater than the inlet temperature. The heated second heating fluid 308 from the ten heat exchangers is flowed through the evaporator 318 of the first ORC. The second heating fluid 308 then combines with the first heating fluid 306, as described previously, to heat the second working fluid 328 in the evaporator 330. Heat from the heated second heating fluid 308 heats the working fluids 316 and 328 of the first and second ORCs, thereby increasing the working fluid temperatures and evaporating the working fluids 316 and 328. The heat exchange with the working fluids 316 and 328 results in a decrease in the temperature of the second heating fluid 308. The combined flow of the first and second heating fluids 306 and 308 is then collected in a heating fluid tank 310 and can be pumped, by a pump 312, back through the seventeen heat exchangers of the first and second heating fluid circuits 302 and 304 to restart the waste heat recovery cycle. As illustrated, the heating fluids 306 and 308 are separated downstream of the pump 312.

The heating fluid circuits 302 and 304 to flow heating fluids 306 and 308 through the seventeen heat exchangers can include multiple valves that can be operated manually or automatically. For example, the NGL fractionation plant can be fitted with the heating fluid flow pipes and valves. An operator can manually open each valve in the circuit to cause the heating fluids 306 and 308 to flow through the circuits 302 and 304, respectively. To cease waste heat recovery, for example, to perform repair or maintenance or for other reasons, the operator can manually close each valve in the circuits 302 and 304. Alternatively, a control system, for example, a computer-controlled control system, can be connected to each valve in the circuits 302 and 304. The control system can automatically control the valves based, for example, on feedback from sensors (for example, temperature, pressure or such sensors), installed at different locations in the circuits 302 and 304. The control system can also be operated by an operator.

In the manner described earlier, the heating fluids 306 and 308 can be looped through the seventeen heat exchangers to recover heat that would otherwise go to waste in the NGL fractionation plant, and to use the recovered waste heat to operate the power generation systems 314 and 326. By doing so, an amount of energy needed to operate the power generation systems 314 and 326 can be decreased while obtaining the same or substantially similar power output from the power generation systems 314 and 326. For example, the power output from the power generation systems 314 and 326 that implements the waste heat recovery network can be higher or lower than the power output from a power generation system that does not implement the waste heat recovery network. Where the power output is less, the difference may not be statistically significant. Consequently, a power generation efficiency of the NGL fractionation plant can be increased.

FIG. 1A illustrates an example dual-ORC power generation system 300 that uses, for example, iso-butane as the working fluid 316 at a high pressure of about 15 to 17 bar and as the working fluid 328 at a low pressure of about 6 to 8 bar to generate about 37 MW of power. The heating fluid 308 (for example, hot oil or water) at about 240° F. from the second heating fluid circuit 304 in the NGL fractionation plant is used in a high pressure cycle (power generation system 314) to preheat and vaporize the high pressure working fluid 316 that flows to the gas expander 320 to generate about 17 MW of power. The ten heat exchangers of the second heating fluid circuit 304 have about 650 MM BTU/h of thermal load of waste heat recovered from the heating fluid 308 that collects this thermal energy from specific units in the NGL fractionation plant. This heating fluid 308 at about 240° F. is cooled down in the evaporator 318 of the power generation system 314 to about 160° F. At this temperature, the heating fluid 308 joins the heating fluid 306 of the first heating fluid circuit 302.

The combined heating fluids 306 and 308, at about 160° F. is used in the evaporator 330 to preheat and vaporize the low pressure working fluid 328 that flows to the gas expander 332 to generate about 20 MW of power. The seventeen heat exchangers of the first and second heating fluid circuits 302 and 304 have about 2350 MM BTU/h of waste heat recovered from specific units in the NGL fractionation plant.

The second heating fluid 308 at a temperature of about 240° F. is used to preheat and vaporize the high pressure working fluid 316 that flows to the gas expander 320 to generate about 17 MW of power. The superheated vapor of the working fluid 316 leaving the gas expander 320 is then combined with the vapor of the working fluid 328 exiting the gas expander 332 and both are condensed using the condenser 322 (for example, with water as a cooling medium at 77° F.). The condensed working fluids 316 and 328 are then pumped back to the two cycle operating pressures using respective pumps 324 and 334, and the cycles continue in evaporators 318 and 330.

FIG. 1B shows the first heat exchanger 302 a in a deethanizer section of the NGL fractionation plant. In this example, the heat exchanger 302 a is positioned and thermally coupled to a heat source to recover waste heat from the refrigeration compressor(s) of the deethanizer reflux generation unit(s). The heating fluid 306 is circulated from the tank 310 at 113° F. to heat exchanger 302 a to cool down the outlet stream of the deethanizer refrigeration compressor. The heating fluid 306 is heated in the heat exchanger 302 a to between about 177° F. and 187° F., for example, about 182° F. before it flows to a collection header to join other heating fluid streams 306 from other parts of the NGL fractionation plant to flow to the evaporator 330 of the power generation system 326. The total thermal duty of the heat exchanger 302 a is about 479 MM BTU/H.

FIG. 1C shows the first heat exchanger 304 a in a propane dehydrator section of the NGL fractionation plant. In this example, the heat exchanger 304 a is positioned and thermally coupled to a heat source to recover waste heat from the propane dehydration section. The heating fluid 308 is circulated from the storage tank 310 at 113° F. to heat exchanger 304 a to cool down the outlet stream of the propane dehydrator. The heating fluid 308 is heated in the heat exchanger 304 a to between about 390° F. and 400° F., for example, about 395° F. before it is circulated to the collection header to join other heating fluid streams 308 from other parts of the NGL fractionation plant to flow to the evaporator 318 of the power generation system 314. The total thermal duty of the heat exchanger 304 a is about 96 MM BTU/H.

FIG. 1D shows the second heat exchanger 302 b in a depropanizer section of the NGL fractionation plant. In this example, the heat exchanger 302 b is positioned and thermally coupled to a heat source to recover waste heat from the depropanizer section. The heating fluid 306 is circulated from the storage tank 310 at 113° F. to heat exchanger 302 b to cool down the outlet stream of the depropanizer overhead stream. The heating fluid 306 is heated in the heat exchanger 302 b to between about 129° F. and 139° F., for example, about 134° F. before it is circulated to the collection header to join other heating fluid streams 306 from other parts of the NGL fractionation plant to flow to the evaporator 330 of the power generation system 326. The total thermal duty of the heat exchanger 302 b is about 951 MM BTU/H.

FIG. 1E shows the second heat exchanger 304 b in a butane dehydrator section of the NGL fractionation plant. In this example, the heat exchanger 304 b is positioned and thermally coupled to a heat source to recover waste heat from the butane dehydration section. The heating fluid 304 is circulated from the storage tank 310 at 113° F. to heat exchanger 304 b to cool down the outlet stream of the butane dehydrator. The heating fluid 308 is heated in the heat exchanger 304 b to between about 390° F. and 400° F., for example, about 395° F. before it is circulated to the collection header to join other heating fluid streams 308 from other parts of the NGL fractionation plant to flow to the evaporator 318 of the power generation system 314. The total thermal duty of the heat exchanger 302 b is about 47 MM BTU/H.

FIG. 1F shows the third heat exchanger 302 c and the third heat exchanger 304 c in a debutanizer section of the NGL fractionation plant. In this example, the heat exchangers 302 c and 304 c are positioned and thermally coupled to respective heat sources to recover waste heat from the debutanizer section. The heating fluid 306 is circulated from the storage tank 310 at 113° F. to heat exchanger 302 c to cool down the outlet stream of the debutanizer overhead stream. The heating fluid 306 is heated in the heat exchanger 302 c to between about 147° F. and 157° F., for example, about 152° F. before it is circulated to the collection header to join other heating fluid streams 306 from other parts of the NGL fractionation plant then directed to flow to the evaporator 330 of the power generation system 326. The total thermal duty of the heat exchanger 302 c is about 587 MM BTU/H.

The heating fluid 308 is circulated from the storage tank 310 at 113° F. to heat exchanger 304 c to cool down the outlet stream of the debutanizer bottoms. The heating fluid 308 is heated in the heat exchanger 304 c to between about 256° F. and 266° F., for example, about 261° F. before it is circulated to the collection header to join the other heating fluid streams 308 from other parts of the NGL fractionation plant then directed to flow to the evaporator 318 of the power generation system 314. The total thermal duty of the heat exchanger 304 c is about 56 MM BTU/H.

FIG. 1G shows the fourth heat exchanger 302 d in a depentanizer section of the NGL fractionation plant. In this example, the heat exchanger 302 d is positioned and thermally coupled to a heat source to recover waste heat from the depentanizer section. The heating fluid 306 is circulated from the storage tank 310 at 113° F. to heat exchanger 302 d to cool down the outlet stream of the depentanizer overhead stream. The heating fluid 306 is heated in the heat exchanger 302 d to between about 160° F. and 170° F., for example, about 165° F. before it is circulated to the collection header to join other heating fluid streams 306 from other parts of the NGL fractionation plant then directed to flow to the evaporator 330 of the power generation system 326. The total thermal duty of the heat exchanger 302 d is about 100 MM BTU/H.

FIG. 1H shows the fourth heat exchanger 304 d and the fifth heat exchanger 304 e in a solvent regeneration section of the NGL fractionation plant. In this example, the heat exchangers 304 d and 304 e are positioned and thermally coupled to respective heat sources to recover waste heat from the ADIP regeneration section. The heating fluid 308 is circulated from the storage tank 310 at 113° F. to heat exchanger 304 d to cool down the outlet stream of the ADIP regeneration section overhead stream. The heating fluid 308 is heated in the heat exchanger 304 d to between about 222° F. and 232° F., for example, about 227° F. before it is circulated to the collection header to join other heating fluid streams 308 from other parts of the NGL fractionation plant then directed to flow to the evaporator 318 of the power generation system 314. The total thermal duty of the heat exchanger 304 d is about 18 MM BTU/H.

Another branch of the heating fluid 308 is circulated from the storage tank 310 at 113° F., to heat exchanger 302 i to cool down the outlet stream of the ADIP regeneration section bottoms. The heating fluid 308 is heated in the heat exchanger 304 e to between about 166° F. and 176° F., for example, about 171° F. before it is circulated to the collection header to join the other heating fluid streams 308 from other parts of the NGL fractionation plant then directed to flow to the evaporator 318 of the power generation system 314. The total thermal duty of the heat exchanger 304 e is about 219 MM BTU/H.

FIG. 1I shows the fifth heat exchanger 302 e and the sixth heat exchanger 304 f in a natural gasoline decolorizing section of the NGL fractionation plant. In this example, the heat exchangers 302 e and 304 f are positioned and thermally coupled to respective heat sources to recover waste heat from the natural gasoline decolorizing section. The heating fluid 306 is circulated from the storage tank 310 at 113° F. to heat exchanger 302 e to cool down the outlet stream of the natural gasoline decolorizing section pre-flash drum overhead stream. The heating fluid 306 is heated in the heat exchanger 302 e to between about 206° F. and 216° F., for example, about 211° F. before it is circulated to the collection header to join other heating fluid streams 306 from other parts of the NGL fractionation plant then directed to flow to the evaporator 330 of the power generation system 326. The total thermal duty of the heat exchanger 302 e is about 107 MM BTU/H.

The heating fluid 308 is circulated from the storage tank 310 at 113° F. to heat exchanger 304 f to cool down the outlet stream of the natural gasoline decolorizer overhead stream. The heating fluid 308 is heated in the heat exchanger 304 f to between about 224° F. and 234° F., for example, about 229° F. before it is circulated to the collection header to join the other heating fluid streams 308 from other parts of the NGL fractionation plant then directed to flow to the evaporator 318 of the power generation system 314. The total thermal duty of the heat exchanger 304 f is about 53 MM BTU/H.

FIG. 1J shows the seventh heat exchanger 304 g in a propane tank recovery section of the NGL fractionation plant. In this example, the heat exchanger 304 g is positioned and thermally coupled to a heat source to recover waste heat from the propane tank vapor recovery section. The heating fluid 308 is circulated from the storage tank 310 at 113° F. to heat exchanger 304 g to cool down the outlet stream of the propane vapor recovery compressor stream. The heating fluid 308 is heated in the heat exchanger 304 g to between about 258° F. and 268° F., for example, about 263° F. before it is circulated to the collection header to join other heating fluid streams 308 from other parts of the NGL fractionation plant then directed to flow to the evaporator 318 of the power generation system 314. The total thermal duty of the heat exchanger 304 g is about 29 MM BTU/H.

FIG. 1K shows the sixth heat exchanger 302 f in a propane product refrigeration section of the NGL fractionation plant. In this example, the heat exchanger 302 f is positioned and thermally coupled to a heat source to recover waste heat from the propane product refrigeration section. The heating fluid 306 is circulated from the storage tank 310 at 113° F. to heat exchanger 302 f to cool down the outlet stream of the propane refrigeration compressor stream. The heating fluid 306 is heated in the heat exchanger 302 f to between about 187° F. and 197° F., for example, about 192° F. before it is circulated to the collection header to join other heating fluid streams 306 from other parts of the NGL fractionation plant then directed to flow to the evaporator 318 of the power generation system 326. The total thermal duty of the heat exchanger 302 f is about 81 MM BTU/H.

FIG. 1L shows the eighth heat exchanger 304 h in a propane product sub-cooling section of the NGL fractionation plant. In this example, the heat exchanger 304 h is positioned and thermally coupled to a heat source to recover waste heat from the propane product sub-cooling section. The heating fluid 308 is circulated from the storage tank 310 at 113° F. to heat exchanger 304 h to cool down the outlet stream of the propane main compressor stream. The heating fluid 308 is heated to between about 232° F. and 242° F., for example, about 237° F. before it is circulated to the collection header to join other heating fluid streams 308 from other parts of the NGL fractionation plant then directed to flow to the evaporator 318 of the power generation system 314. The total thermal duty of the heat exchanger 304 h is about 65 MM BTU/H.

FIG. 1M shows the seventh heat exchanger 302 g in a butane product refrigeration section of the NGL fractionation plant. In this example, the heat exchanger 302 g is positioned and thermally coupled to a heat source to recover waste heat from the butane product refrigeration section. The heating fluid 306 is circulated from the storage tank 310 at 113° F. to heat exchanger 302 g to cool down the outlet stream of the butane refrigeration compressor stream. The heating fluid 306 is heated in the heat exchanger 302 g to between about 142° F. and 152° F., for example, about 147° F. before it is circulated to the collection header to join other heating fluid streams 306 from other parts of the NGL fractionation plant then directed to flow to the evaporator 330 of the power generation system 326. The total thermal duty of the heat exchanger 302 g is about 49 MM BTU/H.

FIG. 1N shows the ninth heat exchanger 304 i in an ethane production section of the NGL fractionation plant. In this example, the heat exchanger 304 i is positioned and thermally coupled to a heat source to recover waste heat from the ethane production section. The heating fluid 308 is circulated from the storage tank 310 at 113° F. to heat exchanger 304 i to cool down the outlet stream of the ethane dryer during the generation mode. The heating fluid 308 is heated in the heat exchanger 304 i to between about 405° F. and 415° F., for example, about 410° F. before it is circulated to the collection header to join other heating fluid streams 308 from other parts of the NGL fractionation plant then directed to flow to the evaporator 318 of the power generation system 314. The total thermal duty of the heat exchanger 304 i is about 22 MM BTU/H.

FIG. 1O shows the tenth heat exchanger 304 j in a natural gasoline vapor section of the NGL fractionation plant. In this example, the heat exchanger 304 j is positioned and thermally coupled to a heat source to recover waste heat from the natural gasoline vapor pressure control section. The heating fluid 308 is circulated from the storage tank 310 at 113° F. to heat exchanger 304 j to cool down the outlet stream of the Reid vapor pressure control column overhead stream. The heating fluid 308 is heated in the heat exchanger 304 j to between about 206° F. and 216° F., for example, about 211° F. before it is circulated to the collection header to join other heating fluid streams 308 from other parts of the NGL fractionation plant then directed to flow to the evaporator 318 of the power generation system 314. The total thermal duty of the heat exchanger 304 j is about 36 MM BTU/H.

FIGS. 1A-1O illustrate schematic views of an example system 300 for a power conversion network that includes waste heat sources associated with a NGL fractionation plant. In this example system 300, a mini-power plant synthesis uses two heating circuits of power generation systems 314 and 326, sharing hot water (or other heating fluid) and isobutane systems infrastructure, to generate power from specific portions of NGL fractionation plant low-low grade waste heat sources. In some aspects, the system 300 can be implemented in one or more steps, where each phase can be separately implemented without hindering future steps to implement the system 300. In some aspects, a minimum approach temperature across a heat exchanger used to transfer heat from a heat source to a working fluid (for example, water) can be as low as 3° C. or may be higher. Higher minimum approach temperatures can be used in the beginning of the phases at the expense of less waste heat recovery and power generation, while reasonable power generation economics of scale designs are still attractive in the level of tens of megawatts of power generation.

In some aspects of system 300, optimized efficiency is realized upon using a minimum approach temperature recommended for the specific heat source streams used in the system design. In such example situations, optimized power generation can be realized without re-changing the initial topology or the sub-set of low grade waste heat streams selected/utilized from the NGL fractionation plant utilized in an initial phase. System 300 and its related process scheme can be implemented for safety and operability through dual ORC systems using buffer streams such as hot oil or high pressure hot water systems or a mix of specified connections among buffer systems. The low-low grade waste-heat-to-power-conversion (for example, less than the low grade waste heat temperature defined by U.S. Department of Energy DOE as 232° C.) may be implemented using the dual ORC systems using isobutane as an organic fluid at specific operating conditions.

The techniques to recover heat energy generated by the NGL fractionation plant described previously can be implemented in at least one or both of two example scenarios. In the first scenario, the techniques can be implemented in an NGL fractionation plant that is to be constructed. For example, a geographic layout to arrange multiple sub-units of an NGL fractionation plant can be identified. The geographic layout can include multiple sub-unit locations at which respective sub-units are to be positioned. Identifying the geographic layout can include actively determining or calculating the location of each sub-unit in the NGL fractionation plant based on particular technical data, for example, a flow of petrochemicals through the sub-units starting from raw natural gas or crude petroleum and resulting in refined natural gas. Identifying the geographic layout can alternatively or in addition include selecting a layout from among multiple previously-generated geographic layouts. A first subset of sub-units of the petrochemical refining system can be identified. The first subset can include at least two (or more than two) heat-generating sub-units from which heat energy is recoverable to generate electrical power. In the geographic layout, a second subset of the multiple sub-unit locations can be identified. The second subset includes at least two sub-unit locations at which the respective sub-units in the first subset are to be positioned.

A first power generation system to recover heat energy from the sub-units in the first subset is identified. The first power generation system can be substantially similar to the first power generation system described earlier. In the geographic layout, a first power generation system location can be identified to position the first power generation system. At the identified first power generation system location, a heat energy recovery efficiency is greater than a heat energy recovery efficiency at other locations in the geographic layout.

A second power generation system to recover heat energy from the sub-units in the second subset is identified. The second power generation system can be substantially similar to the second power generation system described earlier. In the geographic layout, a second power generation system location can be identified to position the second power generation system. At the identified second power generation system location, a heat energy recovery efficiency is greater than a heat energy recovery efficiency at other locations in the geographic layout.

The NGL fractionation plant planners and constructors can perform modeling or computer-based simulation experiments, or both, to identify an optimal location for the power generation system to maximize heat energy recovery efficiency, for example, by minimizing heat loss when transmitting recovered heat energy from the at least two heat-generating sub-units to the power generation system. The NGL fractionation plant can be constructed according to the geographic layout by positioning the multiple sub-units at the multiple sub-unit locations, positioning the power generation system at the power generation system location, interconnecting the multiple sub-units with each other such that the interconnected multiple sub-units are configured to refine natural gas or crude oil, interconnecting the first power generation system with the sub-units in the first subset such that the first power generation system is configured to recover heat energy from the sub-units in the first subset and to provide the recovered heat energy to the first power generation system, and interconnecting the second power generation system with the sub-units in the second subset such that the second power generation system is configured to recover heat energy from the sub-units in the second subset and to provide the recovered heat energy to the second power generation system. The power generation systems are configured to generate power using the recovered heat energy.

In the second scenario, the techniques can be implemented in an operational NGL fractionation plant. In other words, the power generation systems described earlier can be retrofitted to an already constructed and operational NGL fractionation plant.

The economics of industrial production, the limitations of global energy supply, and the realities of environmental conservation are concerns for all industries. It is believed that the world's environment has been negatively affected by global warming caused, in part, by the release of GHG into the atmosphere. Implementations of the subject matter described here can alleviate some of these concerns, and, in some cases, prevent certain NGL fractionation plants, which are having difficulty in reducing their GHG emissions, from having to shut down. By implementing the techniques described here, specific portions in an NGL fractionation plant or an NGL fractionation plant, as a whole, can be made more efficient and less polluting by carbon-free power generation from specific portions of low grade waste heat sources.

Thus, particular implementations of the subject matter have been described. Other implementations are within the scope of the claims provided in this document. 

1. (canceled)
 2. A system, comprising: a first heating fluid circuit configured to thermally couple a first heating fluid to a first plurality of heat sources of a natural gas liquid (NGL) fractionation plant, the first heating fluid circuit comprising a first plurality of heat exchangers fluidly coupled in parallel; a second heating fluid circuit configured to thermally couple a second heating fluid to a second plurality of heat sources of the NGL fractionation plant, the second heating fluid circuit comprising a second plurality of heat exchangers fluidly coupled in parallel; a first evaporator that thermally couples the first heating fluid circuit to a first working fluid to heat the first working fluid with the first heating fluid; a first expander configured to generate electrical power from the heated first working fluid; a second evaporator that thermally couples the first and second heating fluid circuits to a second working fluid to heat the second working fluid with the first heating fluid and the second heating fluid; a second expander configured to generate electrical power from the heated second working fluid; a condenser that thermally couples the first and second working fluids to a condenser supply liquid to cool the first and second working fluids; a heating fluid tank that fluidly couples the first and second heat fluid circuits; and a flow control system that comprises a first set of control valves to selectively thermally couple the first heating fluid to the first plurality of heat sources of the NGL fractionation plant, the control system further comprising a second set of control valves to selectively thermally couple the second heating fluid to the second plurality of heat sources of the NGL fractionation plant.
 3. The system of claim 2, wherein the heating fluid tank fluidly couples the first and second evaporators.
 4. The system of claim 2, wherein at least one of the first or second working fluids is isobutane.
 5. The system of claim 2, wherein at least one of the first or second heating fluids is water or oil.
 6. The system of claim 2, further comprising: a heating fluid pump fluidly coupled to the first and second heating fluid circuits and the heating fluid tank; a first evaporator pump fluidly coupled to the first evaporator to circulate the first working fluid through the first evaporator; and a second evaporator pump fluidly coupled to the second evaporator to circulate the second working fluid through the second evaporator.
 7. The system of claim 6, wherein the first and second working fluids are combined in the condenser.
 8. The system of claim 7, wherein each of the first and second evaporator pumps are positioned downstream of the condenser.
 9. The system of claim 6, wherein the heating fluid pump is positioned downstream of the heating fluid tank.
 10. The system of claim 2, wherein the first and second heating fluids are combined between the first and second evaporators, and the first and second heating fluids are separated downstream of the heating fluid tank.
 11. The system of claim 2, wherein the first plurality of heat sources comprise a first portion of first sub-units of the NGL fractionation plant that comprises an ethane system, a second plurality of first sub-units of the NGL fractionation plant that comprises a propane system, a third portion of first sub-units of the NGL fractionation plant that comprises a butane system, a fourth portion of first sub-units of the NGL fractionation plant that comprises a natural gasoline system, and a fifth portion of first sub-units of the NGL fractionation plant that comprises a solvent regeneration system; and the second plurality of heat sources comprise a first portion of second sub-units of the NGL fractionation plant that comprises the ethane system, a second plurality of second sub-units of the NGL fractionation plant that comprises the propane system, a third portion of second sub-units of the NGL fractionation plant that comprises the butane system, a fourth portion of second sub-units of the NGL fractionation plant that comprises a pentane system, and a fifth portion of second sub-units of the NGL fractionation plant that comprises the natural gasoline system.
 12. A method, comprising: circulating a first heating fluid through a first heating fluid circuit to thermally couple the first heating fluid to a first plurality of heat sources of a natural gas liquid (NGL) fractionation plant, the first heating fluid circuit comprising a first plurality of heat exchangers fluidly coupled in parallel; circulating a second heating fluid through a second heating fluid circuit to thermally couple the second heating fluid to a second plurality of heat sources of the NGL fractionation plant, the second heating fluid circuit comprising a second plurality of heat exchangers fluidly coupled in parallel; heating, with the first heating fluid, a first working fluid in a first evaporator that thermally couples the first heating fluid circuit to the first working fluid; generating electrical power with a first expander from the heated first working fluid; heating, with the first and second heating fluids, a second working fluid in a second evaporator that thermally couples the first and second heating fluid circuits to the second working fluid; generating electrical power with a second expander from the heated second working fluid; cooling the first and second working fluids in a condenser that thermally couples the first and second working fluids to a condenser liquid supply fluid; circulating the first and second heating fluids to combine in a heating fluid tank; actuating, with a flow control system, a first set of control valves to selectively thermally couple the first heating fluid to the first plurality of heat sources of the NGL fractionation plant; and actuating, with the flow control system, a second set of control valves to selectively thermally couple the second heating fluid to the second plurality of heat sources of the NGL fractionation plant.
 13. The method of claim 12, further comprising fluidly coupling the heating fluid tank to the first and second evaporators.
 14. The method of claim 12, wherein at least one of the first or second working fluids is isobutane.
 15. The method of claim 12, wherein at least one of the first or second heating fluids is water or oil.
 16. The method of claim 12, further comprising: circulating the first and second heating fluids through the respective first and second heating fluid circuits with a heating fluid pump fluidly coupled to the heating fluid tank; circulating the first working fluid through the first evaporator with a first evaporator pump; and circulating the second working fluid through the second evaporator with a second evaporator pump.
 17. The method of claim 16, further comprising fluidly combining the first and second working fluids in the condenser.
 18. The method of claim 17, further comprising fluidly separating the first and second working fluids at or upstream of the first and second evaporator pumps.
 19. The method of claim 16, wherein the heating fluid pump is positioned downstream of the heating fluid tank.
 20. The method of claim 12, further comprising: fluidly combining the first and second heating fluids between the first and second evaporators; and fluidly separating the first and second heating fluids downstream of the heating fluid tank.
 21. The method of claim 12, wherein the first plurality of heat sources comprise a first portion of first sub-units of the NGL fractionation plant that comprises an ethane system, a second plurality of first sub-units of the NGL fractionation plant that comprises a propane system, a third portion of first sub-units of the NGL fractionation plant that comprises a butane system, a fourth portion of first sub-units of the NGL fractionation plant that comprises a natural gasoline system, and a fifth portion of first sub-units of the NGL fractionation plant that comprises a solvent regeneration system; and the second plurality of heat sources comprise a first portion of second sub-units of the NGL fractionation plant that comprises the ethane system, a second plurality of second sub-units of the NGL fractionation plant that comprises the propane system, a third portion of second sub-units of the NGL fractionation plant that comprises the butane system, a fourth portion of second sub-units of the NGL fractionation plant that comprises a pentane system, and a fifth portion of second sub-units of the NGL fractionation plant that comprises the natural gasoline system. 